Abstract: We propose to obtain deep K_s-band photometry for 15 clusters at z\le 0.3 at the KPNO 2.1m with FLAMINGOS. These clusters are selected from a large sample which spans a broad range in both mass and redshift (0.04 \le z \le 1). The sample is designed to study the correlation between the total galaxy near-IR luminosity and the cluster binding mass, whose existence has been suggested from studies of nearby clusters. The observations of these low-z clusters will significantly improve our knowledge on the faint-end of the near-IR luminosity function in clusters, which is critical to deriving the light-mass relation. Combined with the data for clusters at higher redshifts already available to us, we will be able to study the light-mass relation at different cosmic epochs, and all the clusters in our sample will serve as mass calibrators for a large, deep near-IR NOAO survey being carried out by Elston \it et al. at 2.1m+FLAMINGOS. The mass calibration is important for such large surveys because their yields make it unfeasible to obtain cluster mass estimates via traditional estimators. Therefore simpler mass indicators such as the total galaxy near-IR luminosity are necessary.